The present invention relates to an electric vehicle control device in both an alternating current (AC) section and a direct current (DC) section. The electric vehicle employs a pulse width modulation (PWM) converter in a propulsion circuit for converting AC power supplied from the AC section to a constant DC power and a variable voltage variable frequency (VVVF) inverter for converting the DC power from the converter to a desired AC power for an induction drive motor. The electric vehicle also employs an inner DC supply line, which directly takes in the DC power from the DC section and supplies to the inverter.
As shown in FIG. 1, a conventional electric vehicle control device in both an AC section and a DC section is provided with a propulsion circuit comprising power supply switching circuit 6 for switching and taking in AC power in the AC section or DC power in the DC section through current collector 1, main transformer 7 for transforming the AC power supplied through current collector 1, PWM converter 2 connected to the secondary side of main transformer 7 through breaker unit 8 for converting the transformed AC power from main transformer 7 into a constant DC power, high speed circuit breaker 9 connected to a DC output terminal of power supply switching circuit 6, filter reactor 10, and filter capacitor 11 connected to the output of filter reactor 10 at a DC output side of PWM converter 2. The propulsion circuit further comprises VVVF inverter 3, a DC input side of which is connected to filler capacitor 11, and induction drive motor (IM) 4 driven by an AC output of VVVF inverter 3. The system is also provided with control circuit 12 for the purpose of gate control to PWM converter 2 and VVVF inverter 3, static inverter (SIV) 5 as an auxiliary power supply, motor speed detector 13 like a pulse generator (PG), voltage detector (V) 14 for detecting a voltage of filter capacitor 11, and motor current detector 15 for detecting a current of each phase line U, V and W distributed between VVVF inverter 11 and induction drive motor 4.
As shown in FIG. 2, the conventional control circuit 12 for gate control of converter 2 and inverter 3 comprises percent modulation operating unit (PMDOP) 12A for calculating a percent modulation which is to determine an output voltage of inverter 3 to be applied to induction drive motor (IM) 4 based on the voltage of filter capacitor 11, damping control component operating unit (DCCOP) 12B for calculating a magnitude of voltage fluctuation of filter capacitor 11, motor current reference operating unit (MCROP) 12C for calculating motor current reference IM* from motor speed reference V* and detected motor speed FR by motor speed detector 13, slip frequency operating unit (SFOP) 12D for calculating slip frequency FS* from the motor current reference IM* output from motor current reference operating unit 12C, and proportional-plus-integral (PI) motor current control component operating unit (PIMCOP) 12E for calculating a motor current control component from motor current reference IM* and effective motor current IM detected by motor current detector 15.
The control circuit 12 further comprises subtraction unit 12F for subtracting effective motor current IM from motor current reference IM*, first adder 12G for adding slip frequency FS* from SFOP 12D and the motor current control component from PIMOP 12E, second adder 12H for adding detected motor speed FR and the output of first adder 12G, third adder 12J for adding the damping control component from DCCOP 12B and calculated slip frequency FS in second adder 12H so as to output inverter frequency reference f.sub.inv *, pulse mode operating unit (PMOP) 12K for calculating a pulse mode, and PWM wave generating unit (PWMGN) 12M for generating an inverter gate control signal based on the percent modulation from PMDOP 12A, the output from PMOP 12K and inverter frequency reference f.sub.inv *.
The control circuit 12 controls gates provided in inverter 3 according to the inverter gate control signal which is generated by PWM wave generating unit 12M.
However, there are drawbacks in the conventional power control. device of the electric vehicle traveling in both the AC section and DC section. In general, VVVF inverter 3 is connected to the output terminal of PWM converter 2 and auxiliary load like static inverter (SIV) 5 is also connected to the output terminal of the converter 2 in the propulsion circuit of the electric vehicle as shown in FIG. 1. An influence of an input filter provided in SIV 5 and a transient behavior of SIV 5 trigger a resonance between a filter coefficient of VVVF inverter 3 and that of SIV 5, causing a ripple of the voltage of filter capacitor 11.
Further, since the electric vehicle travels in both the AC section and DC section, both coefficients of the filter reactor and filter capacitor are to be determined based on electrical characteristics of a power supply substation. While the car is traveling in the AC section with the filter capacitor of a pre-determined capacitance, the ripple voltage of twice higher frequency than that of the AC power supply usually appears on the voltage of filter capacitor 11. While traveling in the DC section, the voltage of filter capacitor 11 fluctuates according to the voltage fluctuation of the DC power supply, directly.
These ripples influence the results of calculation for the percent modulation, the damping control component and the pulse mode operation component because those are derived from calculations based on the voltage of the filter capacitor, causing ripple in the motor current to be controlled by this power control device and also causing the fluctuation of the motor torque. These ripple of the motor current and fluctuation of the motor torque lower comfort for passengers on the electric vehicle. Japanese publication of Patent Application Laid Open No. 62-254691, 1987, discloses a technique of removing the, ripple appearing on the voltage of the inverter in order to resolve the drawbacks of the conventional power control system of the electric vehicle. However, the prior art reference is to be applied to the electric vehicle traveling solely in the AC power supply section. It does not disclose the technique for removing the voltage fluctuation of the filter capacitor caused by the voltage fluctuation of the DC power supply while traveling in the DC power supply section, which causes the fluctuation of the output of the inverter to be applied to the induction drive motor. Accordingly, an improvement of comfort for the electric vehicle traveling in both the AC and DC sections is still remained as a problem in the field.
Furthermore, the power control system is generally to be mounted on the electric vehicle so that it is required to be compact in size and light in weight. The size and mass of the PWM converter and VVVF inverter correlate with the magnitude of DC voltage and input/output current to be applied in each circuit element. The higher the rated DC voltage is raised, the larger the snubber loss and switching loss in the switching elements increase. Then, as the result, it becomes necessary to make peripheral circuit elements of the propulsion circuit larger in size and heavier in mass, and consequently to make a cooling system which is to be necessary for the propulsion circuit larger. Moreover, the larger the rated input/output current is raised, the larger elements the system comes to require, so that the steady loss of the elements increases and the size of the cooling system should be enlarged. Therefore, it is important to select a suitable magnitude of the DC voltage and the input/output current. However, in the conventional power control device, the voltage and current are determined based on the rated voltage of the DC section so that the requirement for downsizing the cooling system is still remained as a problem.